Towing hook for seaplanes



Feb. 10, 1959 -Tp M. KUREK ET A1 TOWING HOOK'FOR SEAPLANES Filed Jan. 31, 1956 s shets-sneet 1 lINVENTORS DANIEL C. JONES THADDEUS M. KUREK ROBERT G. POPP ATTORNEY T. M. KUREK ET AL TOWING HOOK FOR SEAPLANES Feb. 10, 1959 5 Sheets-Sheet 2 Filed Jan. 3l. 1956 V im K m S UP W. KP 00.0 TJMP. muws vLm mDE MM@ DTR M., A. F

ATTORN EY Feb. 10, 1959 T. M, KUREK ET AL 2,872,890

TOWING HOOK FOR SEAPLANES Filed Jan. 31, 195e s sheets-sheet s LATCH uP LATCH DowN l-lookul Hook Down FIG. 6

INVENTORS DANIEL C. JONES THADDEUS M. KUREK ROBERT G. POPP ATTORNEY A United States Patent f() 2,s1'2,s9 o TowING Hoort non SEAPLANES Thaddeus lvl. 'Kurcln Idlewylde, and Rollei-tfy G.. Popp, Rosedale, Md., and Daniel C. Jones, CuyahogaFalls, Ohio, assignors to The MartinCompan'yJ corporation of Maryland The present invention relates to devices for securing seaplanes, or so-called flying boats, to mooring lines or tow lines, for example, and is more particularly concerned with an improved device for mounting in the hull of a seaplane to facilitate the attachment of the plane to a moving tow line supported near the surface of a body of water, and to facilitate the subsequent release of the plane from the line. Y .e v In many instances it is `desirable to provide for the refueling of seaplanes at sea, so that the effective range thereof may be increased. For this purpose,a `fuel ship or `surfaced submarine trails a tow line, to which the seaplane is attached during refueling. The `,present invention seeks to provide an improved hook mechanism which is mounted in the hull of the seapla'ne whereby the plane may taxi along the surface of the water and pick up and engage a tow line floating at or near the surface of the water and which may be moving.

One of the difficulties encounteredfin; engaging a tow line trailingfrom a moving ship is that the line is not anchored at its trailing end, and it is therefore ynot possible to rely upon any substantial force exerted by the line for actuating the pickup mechanism.- Accordingly, the device of the present invention is of such a nature that a freely floating line may be readily picked up and engaged fwith the plane. In this respect, the .new device includes a switch-adapted to be actuated in response to engagement of the device with the tow line. In one embodiment of the invention the switch energizes a Vpower-device for c1os ine the hook mechanism upon the line.. In .y another embodiment, relying upon manual operation, the switch energizes a signal device for visibl-y or audibly indicating to one of the crew that the line has been engaged, whereupon the hook mechanism is manually closed upon the line. y

Another object of the invention is the provision of a tow line hook mechanism adapted to'withstand the .relatively large forces exerted by the tow line upon the plane when the tending vessel is moving through the Watch-and whichis also so constructed as to permit the line to `be properly released while under tension. To this end, the new device is constructed in such-manner that uponv its closure about the tow line the forces `exerted by the line are absorbed bythe frame structure of the plane and are isolated from certain parts of the actuating mechanism for the device. The new device is arranged so that the operating linkages thereforrare not exposed tothe water, and are at all times accessible from the interior ofthe plane for making repairs. And one or more Shear ,pins are incorperatedin the linkage for releasing the device from the cable if excessiveforces are4 Yapplied by the latter.v The .shear pins form lpart of the linkage which vis accessible from the interior of the plane,vso that replacements may be quickly made when necessary.,

For a better understanding of the invention, reference may be made to the accompanying drawings", inwhich:

Fig. 1 is a simplified representation otra seapla'ne emy 2,872,890 Patented Feb. 10, 195sY ice 2 ploying the new. towing hook for making a connection with a tow line trailing a tending vessel;

Fig. 2 is an enlarged fragmentary section view through the plane, showing the new towing hook and the actuating mechanism therefor;

Fig. 3 is a fragmentary view of the hook and mechanismof Fig. 2, with the parts in a different operating posi-tion;

Fig. 4 is a section view taken on line 4-4 of Fig. 2;

Fig. 5 ,is a fragmentary view of the mechanism of Fig. 2 showing the lever arrangement used in manual operation of the mechanism; and v Fig. 6 is a simplified schematic representation k,of a power system and control circuit which may be employed in connection with the new device. l*

For the purpose of refueling seaplanes at sea a tending vessel 10, which may be aship or surfaced submarine, for example, trails a tow line 11 at or near the surface of the water. A plane 12 may then taxi over the' surface of the water'at an angle to the tow line 11, and upon reaching the line is madefast thereto by means of a hook assembly 13 mounted in the hull vof the planef The hook mechanism of the present invention comprises a hook member 14 which is mounted upon a transverse lshaft 15 journaled in bearings 16 in the hull 17 of the plane. The hull 17 has a recess 18 in its lower center, portion defined by spa-ced side walls 19 and by an upper wall 20. The recess 18 is watertight, and suitable sealing means 21 are provided between the bearings 16 and shaft 15 where the ends of the shaft project through the walls 19.l Thehook-H has a portion 14a which, when the hook is in operative position, extends downwardly from the shaft 15 and has a portion 14h whichprojects forwardly beneath the hull of the plane when the hook is in its' operating position. The recess 1S is of such dimensions that the hook 14 may be pivoted upwardly and rearwardly about the axis of shaft 15 to completely enclose `the' hook within therecess.

Forwardly of'the hook-supporting shaft 15, a second shaft 22 -is journaled in the side walls 19 of the recess. The opposite ends of the shaft 22 extend through the walls 19 and are provided with suitable lsealing means,l

substantially in the same manner asdescribed with respect to the shaft 1S. A latch member 23 is rigidly secured tothe' shaft- 22 between its ends and has an operative position in which it extends downwardly from the hull 17 to the forwardly projecting portion Lib of the hook, as shown in Fig. 2, and an inoperative or retracted position, as shown in Fig. 3, in which itis pivoteti upwardly and forwardly so as tobe entirely enclosed-within `the recess 18.

When both the hook 14 .and latch 23 are in their op` erative positionsjsee Fig. 2,`thcy dene with the bottom of the h'ull v17 a small opening 24 in which the tow-f ingwcable'll `may be received. It is contemplated 'of course that the cable 11 will have one or more enlarged portionsth'roughoutits length so that while the body:

of the cable 11 may be received inthe opening defined by the members 14 and23 lthe enlarged portionsl of the cable 'will not pass 'through 'such'ope'ning. Therefoi'ep when lthe hook mechanism is engaged with the tow line 11 the line will slip through 'the hook opening untilan enlarged portion of theicable reaches the opening, where-ik upon the hook 'will be rmly engaged with the line.

For actuating the hook 14,' a pair of crank arms 25.Y

are rigidly secured to the' outer ends of the hook shaft 1S., outwardly of the walls 19. The crank arms 25 are pivotally connected at their outer ends to links 26, ,which are in turn pivotally connected to arms 27a of a bell crank. Thearms 27a are vrigidly secured atwtheiruppen ends. to the oppositesends cfa ,transverse'shaft 28 eXtend-.;,

ing through the walls 19 at a point above the upper wall 20' of the chamber 18. An upper bell crank arm 27b is lrigidly secured to the shaft 28 intermediate the walls 19.and pivotally connects at its outer end with an upwardly extending control rod 29. The rod 29 may be of any suitable length, and extends upwardly to the cockpit or other control station in the plane., At its upper end, the control rod 29 is pivotally connected to a crank arm 30, secured to a tubular shaft 31, the latter being journalcd in bearings 32, 33 mounted in the framework of the plane. One end of the shaft 31 extends outwardly of the bearings 33 and connects, in a manner to be more fully described, with an operating lever 34.

At the upper ends of the bell crank arms 27a there are short arms 35 to which coil springs 36 are secured at one end. The other ends of the springs 36 are secured to brackets 37 iixedly mounted tov the frame of the plane 12. With the mechanism in the position shown in Fig. 2 the axes of the springs 36 lie above the axis of the bell crank shaft 28, and with the mechanism in the position shown in Fig. 3 the-spring axes lie below that of the shaft 28. The arrangement is such that the springs 36 exert an over-centering moment upon the bell crank 27-28 urging the mechanism into one or the other of the illustrated positions.

As will be observed in Figs. 2 andS, the outer end portion of the control shaft 31 rigidly mounts a quadrant member 38, which is comprised of two angularly disposed arms 38a and 38b. The operating lever 34 is loosely mounted on the shaft 31, by means of a nut 39, for example, and has a driving pin 40 which projects inwardly from the handle and is positioned between the arms `38a clockwise direction will urge the crank arms 27a more firmly against the stop screws 41, so that under no circumstances can the linkage 26--27a break to release the hook 14 at an undesirable time.

It may be expected that due to rough seas or careless handling of the plane 12 or tending vessel 11 excessive forces will occasionally be applied to the hook 14 which might damage the framework of the plane. Accordingly, the links 26 and bell crank arms 27a are connected together by means of frangible bolts 43 which, while being suiciently strong for all normal purposes, will shear upon the application of excessively high force so that the hook 14 is immediately released. -It is important to note in i this respect that the links 26, crank arms 27a, and frangible and 38b of the quadrant 38. When the lever 34 is pivoted on the control shaft 31 it will move freely until the pin 40 engages one of the arms 38a or 38b. Further movement of the lever 34 will cause the quadrant 38 and hence the shaft 31 to rotate. This will shift the hook meehanism toward one of the positions shown in Figs. 2 and 3, causing the springs 36 to move through their over-centering positions. When the springs 36 are moved through their over-centering positions, the hook mechanism is urged into one of the illustrated positions independently of any force applied to the lever 34, and since there is substantial lost motion in between the lever 34 and quadrant 38 the mechanism will freely snap into position. Hence, there is no likelihood of injury to the person operating the lever 34.

When the hook 14 is in its lower or operative position and engaged with a towing cable 11 substantial forces are often exerted upon the hook 14. To isolate these large forces from the control rod 29 and shaft 31, the cranks 25, bell crank 27--28 and links 26 are so proportioned that the links 26 are aligned in a substantially deadcenter relation with bell crank arms 27a when the hook 14 is in its operative position. Thus, any forces tending to rotate the hook in a counterclockwise direction will have little or no tendency to rotate the bell crank 27-28, and therefore such forces will be isolated from the control rod-29. This also avoids accidental snapping over of the manual control lever 34, which might seriously injure crewmembers standing nearby.

In order to securely lock the hook 14 in its operative position, stop-members are provided which are in the form of screws 41 adjustably mounted in brackets 42 secured to side walls 19. The stop screws 41 are adjusted in the brackets 42 so that when the crank arms 27a and links 26 are moved from the positions shown in Fig. 3 through and slightly beyond a dead-center position the crank arms 27a will engage the projecting ends of the stop screws. The springs 36 will then urge crank arms 27a in the direction of the screws 41 to retain the arms 27a inthe desired position.

When the stop screws 41 are adjusted so that the crank arms 27a and links 26 are slightly past a dead-center position, any -forces tending to rotate the hook 14 in a counterconnecting bolts 43 are located in the interior of the plane and the bolts "43 .areltherefore Vreadily accessible so that repairs may be quickly made when necessary.

For actuating the latch member 23, the latch shaft 22 rigidly mounts a pair of crank arms 44 at its outer ends, exteriorly of the walls 19. The arms 44 are connected through links 45 and lrangible bolts 46 to the arms 47a of a bell crank. The bell crank arms 47a are secured at the opposite ends of a transverse shaft 48 journaled in and extending through the walls 19. The shaft 48 mounts a second bell crank arm 47b. The arm 47b is connected through a control rod 49 and crank arm 50 with a control shaft 51 journaled in the bearings 32, 33. A quadrant 52 is secured near one end of the shaft 51, and an operating lever 53 is loosely mounted on the shaft 5l adjacent the quadrant and arranged to engage the same through a pin 54 positioned between the arms 52a and 52h of the quadrant. The operation of the linkage just described is substantially the same as that of the hook actuating mechanism and includes over-centering springs 55 and stop .screws 56 arranged to engage bell crank arms 47a just as the arms 47a and links 45 move through a l dead-center position.

crank 47--48 in a counter-clockwise direction, and there-- by, through the link 45, rotates the latch 23 in a clockwise direction, moving its lower end upwardly and forwardly away from the hook 14. Movement of the hook 14 from its operative position to its inoperative position is also effected by moving the lever 34 in a counterclockwise drection, which moves the control rod downwardly, rotating the bell crank 27--28 in a clockwise direction, and through the links 26 rotating the hook 14 in a counterclockwise direction so that the lower end of the hook moves upwardly and rearwardly away from the latch 23.

When the hook 14 or latch 23 is released and retracted, there may be some tendency ofthe released part to overtravel, due to the ovcrcentering force of the spring or to forces exerted by an engaged mooring or tow line. Thus, to avoid excessive shock forces, the upper wall 20 of the chamber 18 is provided with rubber blocks 67 and 68 to resiliently absorb some of the rebound force, if either the hook or latch overtravels excessively.

When the plane 12 taxis toward the tow line 11, to bc engaged therewith, the hook 14 is lowered, while the latch 23 is retained in its retracted or inoperative position. As the hull of the plane moves over the line 1.1, the linc is picked up bythe hook 14, and thereafter thc latch may be moved into its operative position, closing the hook mechanism upon the tow line. In the past, it has been common practice to employ hook mechanisms of a type adapted for actuation in response to the exertion of a sub'- stantial force upon the hook` by the line engaged. ln such cases, the line engaged was a mooring line or the like xed yat two 4or more points and therefore capable of exerting the forces required. However, for the use herein contemplated the line 11 is attached at one end only and will freely move through the water, so that forces exerted by the line cannot be relied upon for actuating the hook mechanism. Accordingly, in the apparatus of the present invention, the hook 14 carries a trigger-like switch operator 57 which is pivoted on the hook near the upper portion thereof and has a lower leg extending downwardly along the vertical portion 14a of the hook and an upper portion terminating near Ithe upper end of the hook. By means of a spring-pressed plunger 58 recessed in the hook the lower end of the switch operator 57 is urged forwardly with respect to the hook so that the forward edge of the operator 57 lies ahead of the forward edge of the vertical portion 14n of the hook. The upper end of the operator 57 is arranged so that it underlies a switch 60 when the hook is in its operative position. Thus, as the plane taxis across the tow line 11, with the hook 14 in a lowered position, the towing line will be picked up by the hook and the switch operator 57 will be depressed, even though the force exerted by the line 11 is rather small. When the operator 57 is depressed, switch 60 closes and completes an electrical circuit through a switch 75 and signal device 76, which maybe a signal light or buzzer, for example, so that the pilot or crew member of the plane is immediatelyv advised of the fact that the tow line 11 has been engaged. The latch 23 is immediately lowered by appropriate manipulation of the lever 53, and the tow line is thereby properly engaged.

Since the switch operator 57 and the spring-pressed plunger 58 are exposed in the water and may become encrusted with salt or other matter tending to impair the free operation of these members, the plunger 58 has a portion 53a which projects a short distance outwardly of the back edge of the hook 14. When the plunger 58 is depressed the portion 58a will project outwardly even more, and in the event the plunger sticks in this Aposition the projecting portion 58a will engage an abutment screw 59 and be returned thereby when the hook is subsequently retracted into the hull of the plane. By this means it is assured that the operator 57 and plunger 53a will be in proper position when the hook 14 is next lowered for engaging a cable.

In some cases it may be desirable to employ power means in place of or in addition to the levers 34 and 53 for actuating therespective hook and latch operating mechanisms. A simplified arrangement for this purpose is shown in Fig. 6, wherein fluid cylinders V62 and 63 are operatively connected with control shafts 31 and 51, respectively. The cylinders 62 and 63 are controlled by four-way solenoid valves 64 and 65, respectively, and normally condition the fluid cylinders so that the hook and latch members are held in retracted positions. The solenoid valve 64, which controls the hook operating cylinder 62, is connected in series with a power source through a doublethrow switch 66 and circuit breaker 70, .and when the left hand contact of the switch is closed the hook will be lowered into its operating position. When the hook is fully lowered, a switch 7l is engaged andclosed by the linkage mechanism, completing a circuit through a signal light or buzzer 61. This signifies to the operator that the hook is in operative position.

When the tow line or other device is engaged by the hook 14, the operator 57 is depressed, closing switch 60, and completing a circuit through the latter switch and through the energizing coil of a time-open time delay relay 73. The relay 73 is thereby energized, and completes a circuit through the left hand coil of solenoid valve 65. This causes the actuator 63 to be energized to lower the latch 23 into operative position.

As the latch 23 moves into its lower or operative position a switch 72 is moved to open its upper contact and close its lower contact.

latch is closed upon the hook.

It will be observed that the operation of switch 72', 'to open its upper contacts and'close its lower contacts, opens This energizes a signal device 74, which may be a light or buzzer, signifying that the the energization circuit for the time delay relay 73. After a: short delay, which is sucient to insure continued movement of the latch operating linkage through its dead-center position, the contacts of relay 73 open, deenergizing solenoid valve and actuator 63. By virtue of this arrangement, continual energization and de-energization of the valve 65 and actuator 63 due to movement of the line within the hook enclosure is avoided.

To retract the hook and latch mechanisms, for releasing a cable, the switch 66 is movedfto close the right hand contacts thereof. This energizes 'the right hand coils of solenoid valves 64 and 65, admitting fluid to the head end of actuator 62 and rod end of actuator 63, to retract the members 14 and 23 simultaneously. t

It is contemplated that both of the solenoid operate valves 64 and 65 will be of a type capable of manual as well as electrical operation, so that hydraulic operation ofthe hook and latch mechanisms will be possible, even in the event of failure of the energizing circuits for the valves.

To retract the hook and latch manually, the levers 34 and 53 are moved in a counterclockwise direction,.as viewed in Fig. 5. To facilitate this operation, the hook operating lever 34 is provided with a bracket 77 mounting a pick-up arm 78,'which engages the latch operating lever 53, so that the latter is carried into release position by movement of the hook operating lever alone. This arrangement also facilitates the operation of manually moving of the hook into its operative position, since the operator may readily determine which of the levers 34 or 53 should be operated. Thus, if the latch operating lever 53 is inadvertently grasped for the intended operation of lowering the hook 14, the pick-up arm I8 will be engaged, and the operators error is immediately discovered.

One of the important features of this invention resides in the fact that the hook and latch members are moved toward each other, into operative position for engaging a tow line, by separate linkages which move slightly through dead-center positions. The hook and latch members are firmly locked in their operative positions by means of stop screws 41 and 56, regardless of the magnitude of the forces applied by the tow line and regardless of the direction of such forces unless, of course, the forces become so excessive as would tend to damage the framework of the plane, in which case the frangible connecting bolts 43 and 46 will be sheared to quickly release the cable. Since the hook and latch members move toward each other into cable-engaging positions the cable may be readily released at any time, regardless of the direction in which force is applied by the cable. ln fact, since any force applied by the cable will tend to separate the hook and latch, such force will actually assist to some extent in releasing the cable.

It will be noted that although forces exerted by the cable upon either the hook 14 or latch 23 will tend to urge the operating linkage for such part against the stop screws associated therewith, this urging force is a small percentage of the force applied by the cable, since the parts are so nearly in a dead-center position, and the linkage may be readily unlocked by manual operation of the levers 34 and 51. For example, the hook mechanism can be readily released manually while the line is exerting thereon a force as high as 16,000 pounds When the hook mechanism is released under high load the force exerted by the'towing cable will force one of the parts 14 or 23 toward its retracted position when the operating linkage for such member passes through its deadcenter position. Thus, another advantageous feature of theinvention resides in the use of a lost motion connection between the control shafts 31 and 51 and the respective. operating levers 34- and 53 therefor so that the operating linkage may override the levers 34 and 53,

thereby avoiding any possible injury of the crew members.`

Another advantage of the new device is the use of a signal mechanism to indicate contactl of the hook 14 with the towing cable 11, even though such contact is relatively light, so that the latch may be immediately moved into operative position to engage the cable.

One of the important features of the invention, from a maintenance standpoint, is that all operating parts except the hook 14, latch 23, and switch operating mechanism are contained in the interior of the plane, out of contact with the water and readily accessible for adjustment or repair when required.

Although the invention has been described with particular reference to use in connection with the mooring or towing of seaplanes, it will be understood that the apparatus has advantageous application for ground towing, beaching, docking and like operations, and reference should be made to the following claims to determine the full scope of the invention.

We claim:

l. A towing hook mechanism for a seaplane or thc like comprising a hook pivotally mounted on the hull of the plane and movable forwardly into an operative position in which the lower portion of the hook extends forwardly below the hull, a latch pivotally mounted on the hull and movable rearwardly into an operative position closing ott the opening into the hook, independently-operable actuating linkages for said hook and latch, said linkages being movable through dead-center positions to move the hook and latch into operative positions, stop means engaging the linkages upon their moving through their respective dead-center positions, and over-center spring means operative when the linkages move to dead-center positions to urge them against their respective stop means, said springs also being operative to urge the hook and latch into a retracted position upon the linkages being drawn through their dead-center positions in a direction away from their respective stop means.

2. A towing hook mechanism for a seaplane or the like comprising a hook mounted on the hull of the plane and having an operative position in which the lower portion of the hook extends forwardly below the hull, a latch pivotally mounted on the hull and movable rearwardly into an operative position closing off the opening into the hook, a signal device, a switch for energizing the signal device, a switch operator mounted to be engaged by an object picked up by the hook and operative upon such engagement to close the switch and energize the signal device, independently-operable actuating linkages for said hook and latch, said linkages being movable through deadcenter positions to move the hook and latch into operative positions, stop means engaging the linkages upon their movingthrough their respective dead-center positions, and over-center spring means operative when the linkages move to dead-center positions to urge them against their respective stop means, said springs also being operative to urge the hook and latch into a retracted position upon the linkages `being drawn through their dead-center positions in a direction away from their respective stop means.

3. A towing hook mechanism for a seaplane or the like comprising a hook mounted on tbe hull of the plane and having a portion extendable forwardly below the hull, a latch pivotally mounted on the hull and movable rearwardly into an operative position closing oi`t` the the open` ing into the forwardly extending portion of the hook, power means for moving the latch into operative position, control means including a switch for energizing the power means, and a switch operator mounted adjacent the hook for engagement with an object to be picked up by the hook, the power means being operative upon engagement of the switch operator with the object to move the latch into operative position.

4. A towing hook mechanism for seaplanes or the iike comprising a hook pivotally mounted on the hull of the plane and movable forwardlyinto an operative position in which a lower portion of the hook extends forwardlyv below thehull, a latch pivotally mounted on the hull and movable rearwardly into operative position closing olf the opening into the lower portion of the hook, independently operable articulate linkages connecting the hook and latch and movable through their deadcenter position to move the hook and latch into operative positions, stop means engaging the linkages upon their moving through their respective dead-center positions, and over-center spring means operative when the linkages move to dead-center positions to urge them against their respective stop means.

5. Apparatus according to claim 4 further characterized by the over-center spring means being operative to urge the hook and latch into retracted position upon the articulate linkages being drawn through their dead-center positions in a direction away from their respective stop means, and further including hand levers for actuating the respective linkages, and lost motion means connecting the hand levers to the linkages whereby upon over-centering of the spring the linkages may move independently of their respective hand levers.

6.In a towing hook mechanism for a seaplane or the like, the combination of a member pivotally mounted on the hull of the plane and movable from a retracted position within the outline of the hull to an operative position below the hull in which the member may be engaged with a towing cable or the like, an articulate linkage for moving the member from its retracted position to its operative position, the linkage moving through its deadcenter position when moving the member into its operative position, stop means engaging the linkage upon movement thereof through its dead-center position to lock the member in operative position, and over-center spring means operative upon the linkage moving to dead-center position to urge the linkage against the stop means.

7. In a towing hook mechanism for a seaplane or the like, the combination of a member pivotally mounted on the hull of the plane and movable from a retracted position within the outline of the hull to an operative position below the hull in which the member may be engaged with a towing cable or the like, an articulate linkage for moving the member from its retracted position to its operative position, the linkage moving through its dead-center position when moving the member into its operative position, stop means engaging the linkage upon movement thereof through its dead-center position to lock the member in operative position, said member comprising a hook, and further including a latch pivoted on the hull and movable toward the hook into an operative position closing off the opening of the hook, a second articulate linkage for moving vthe latch, the second articulate linkage moving through its dead-center position in moving the latch to its operative position, and stop means for engaging the second articulate linkage upon its moving through deadcenter position. v

8. In a towing hook mechanism for a seaplane or the like, the combination of a hull, a hook member, a latch member, each of said members being mounted on said hull for pivotal movement between an active and an inactive position, said hook member having a hook portion which extends below said hull for engagement with a tow cable or the like when said hook member is in its active position, said latch member when in its active position closing ott said hook portion, a rst articulate linkage connected to said hook member, a second articulate linkage connected to said latch member, said members being movable between their active and inactive positions by the respective linkages, each of said linkages including a pair of links connected by a pivot arranged to move through a dead-center position, tirst stop means arranged to engage a portion of said first linkage when said hook member is in its active position and the pivot of said rst link- 4age is offset from dead-center position, second stop means arranged to engage a portion of said second linkage when said latch member is in its active position and the pivot of said second linkage is offset from dead-center position, and

9 19 spring means interconnecting said huil and said rst link- References Cited in the ic of this patent age arranged to maintain said hook member alternatively UNITED STATES PATENTS in its active or inactive position with the pivot of said rst 1 869 506 Richardson Aug 2 1932 linkage correspondingly oiset from the dead-center posi- 5 limi-723 Perkins "n- 'ujune 6 1933 tion, said spring means urging said portion of said first linkage against said rst stop means when said hook mem- FOREIGN PATENTS bei' is in its active position. 102,245 Great Britain NOV. 23, 1916 919,839 France Dec. 16, 1946 

